# betting

Converts odds, strips the vig, finds edge and sizes bets with the Kelly criterion. Useful when you have prices from two sources and want to know if there is value.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1600 installs · ★ 258
- Author: machina-sports
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/machina-sports/sports-skills/tree/HEAD/skills/betting/SKILL.md
- Updated: 2026-10-24
- HTML: https://affpapa.org/en/nevibecode/skills/betting

## What it does

\`betting` is a skill in the `machina-sports/sports-skills` set, and it only does math. It converts odds between American, decimal and probability formats, removes bookmaker margin with `devig`, compares a fair probability against a market price, returns the Kelly fraction, checks for arbitrage, evaluates parlays and reads line movement.

It never fetches odds. Pull them first from a sport-specific skill for ESPN lines or from `polymarket`/`kalshi`, then hand them to the analysis. That is why `devig` comes first in every workflow: comparing a raw sportsbook price to a prediction market price gives you nothing useful. The format string also has to be exact — `american`, `decimal` or `probability` — or the call fails with `ValueError: unknown format`.

Two ways in: the CLI, `sports-skills betting <command>`, or the Python SDK, `from sports_skills import betting`. Commands like `get_odds`, `calculate_ev` and `compare_markets` are not part of this skill; check `references/api-reference.md` for what actually exists. If the Kelly fraction comes back above 0.5, the authors suggest re-checking your fair probability and using half or quarter Kelly instead.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add machina-sports/sports-skills --skill betting -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/betting/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/betting/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add machina-sports/sports-skills --skill betting -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/betting/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add machina-sports/sports-skills --skill betting -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/betting/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install machina-sports/sports-skills betting
```

2. **Manually: put the files in place**
- File: `.github/skills/betting/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add machina-sports/sports-skills --skill betting -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/machina-sports/sports-skills --path skills/betting
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/betting/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add machina-sports/sports-skills --skill betting -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/machina-sports/sports-skills/tree/HEAD/skills/betting/SKILL.md

## When to use it
- turn American odds into an implied probability and decimal price
- strip the vig and get fair probabilities for both sides
- compare an ESPN line with a Polymarket price to find edge
- size a bet with the Kelly criterion
- check whether two venue prices add up to an arbitrage

## Example prompts
- ESPN has the home team at -150 and Polymarket has it at 52 cents. Is there edge?
- De-vig -150,+130 and tell me the optimal bankroll fraction
- Check for arbitrage: Polymarket home at 0.48, Kalshi away at 0.49

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: e199a18ff4fa4381.

BEGIN THIRD-PARTY FILE e199a18ff4fa4381
````text
---
name: betting
description: |
  Betting analysis — odds conversion, de-vigging, edge detection, Kelly criterion, arbitrage detection, parlay analysis, and line movement. Pure computation, no API calls. Works with odds from any source: ESPN (American odds), Polymarket (decimal probabilities), Kalshi (integer probabilities).

  Use when: user asks about bet sizing, expected value, edge analysis, Kelly criterion, arbitrage, parlays, line movement, odds conversion, or comparing odds across sources. Also use when you have odds from ESPN and a prediction market price and want to evaluate whether a bet has positive expected value.
  Don't use when: user asks for live odds or market data — use polymarket, kalshi, or the sport-specific skill to fetch odds first, then use this skill to analyze them.
license: MIT
metadata:
  author: machina-sports
  version: "0.2.0"
---

# Betting Analysis

Before writing queries, consult `references/api-reference.md` for odds formats, command parameters, and key concepts.

## Quick Start

```bash
sports-skills betting convert_odds --odds=-150 --from_format=american
sports-skills betting devig --odds=-150,+130 --format=american
sports-skills betting find_edge --fair_prob=0.58 --market_prob=0.52
sports-skills betting evaluate_bet --book_odds=-150,+130 --market_prob=0.52
sports-skills betting find_arbitrage --market_probs=0.48,0.49
sports-skills betting parlay_analysis --legs=0.58,0.62,0.55 --parlay_odds=600
sports-skills betting line_movement --open_odds=-140 --close_odds=-160
```

Python SDK:
```python
from sports_skills import betting

betting.convert_odds(odds=-150, from_format="american")
betting.devig(odds="-150,+130", format="american")
betting.find_edge(fair_prob=0.58, market_prob=0.52)
betting.find_arbitrage(market_probs="0.48,0.49")
betting.parlay_analysis(legs="0.58,0.62,0.55", parlay_odds=600)
betting.line_movement(open_odds=-140, close_odds=-160)
```

## CRITICAL: Before Any Analysis

CRITICAL: Before calling any analysis command, verify:
- Odds format is correctly identified (american, decimal, or probability).
- ESPN odds are de-vigged with `devig` before computing edge vs prediction market prices.
- This module computes — it does not fetch. Obtain odds from sport-specific skills or polymarket/kalshi first.

## Workflows

### Compare ESPN vs Polymarket/Kalshi

1. Get ESPN moneyline odds (e.g., from `nba get_scoreboard`): Home: `-150`, Away: `+130`
2. Get Polymarket/Kalshi price for the same outcome (e.g., home at `0.52`)
3. De-vig: `devig --odds=-150,+130 --format=american` → Fair: Home 57.9%, Away 42.1%
````
END THIRD-PARTY FILE e199a18ff4fa4381

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